Field of the Invention (Technical Field)
The present invention relates to a geotechnical apparatus equipped for geotechnical investigation comprising a holder with a coiled rod wherein the rod is provided with a probe, such as a penetrometer, and the apparatus comprises a rod bending/straightening device and a drive unit for both uncoiling a the coiled continuous rod and pushing the uncoiled rod with the probe into the ground and for pulling such a rod with the probe out of the ground and recoiling the continuous rod, the apparatus being arranged for operation on land as well as on a sea floor, wherein the drive unit comprises two grippers arranged to alternatingly grip the rod and move it along its longitudinal axis over a predefined length.
Description of Related Art Including Information Disclosed Under 37 C.F.R. §§ 1.97 and 1.98:
U.S. Pat. No. 6,527,055 discloses a coiled tubing injection system for moving coiled tubing into or out of the well bore comprising: a coiled tubing injector; a static tubing gripper having a closed and an open position; and a movable tubing gripper having a closed and an open position, said movable tubing gripper being coaxially reciprocal between a first and a second position; wherein the coiled tubing injector, the static tubing gripper and the movable tubing gripper are positioned coaxially along the length of coiled tubing and are independently selectively operable. This known device is neither intended nor suited for geotechnical investigation, wherein the tubing would be provided with a probe such as a penetrometer.
The known system exhibits a number of disadvantages. The drive system is complex with a large number of moving parts, typically requiring proper sealing against ingress of sea water or debris. Further the uncoiling/coiling operation is rather crude. The uncoiling is accomplished by pulling the rod along a goose neck through a pulling force of the injector heads and supported by a back tension from the reel, while during coiling these roles are reversed. The reel is pulling and the injector heads are providing back tension. This results in most cases that the uncoiled rod will not be quite straight, which need not be a problem in existing wells, because inside the well, the rod is being guided by the wall of the well. The straightness of the rod obtained by the existing process is however clearly insufficient in geotechnical investigations wherein the rod is pushed into the ground without additional support and guiding. Also when recoiling wherein the pulling force is exerted by the reel, this results in a coil that requires additional holding elements added to the reel to maintain the coil diameter as soon as the back pulling disappears. These additional holding elements add to the complexity of the reel.
In addition, because the straightening as well as the coiling is accomplished by pulling the coil along the goose neck, this pulling force is relatively large and may lead to diameter changes of the rod. Also, the point contact of the drive unit with the rod during pushing and pulling requires a rather high maximum contact force applied at the rod to obtain sufficient friction to drive the rod. The probability of cold deformation of the rod to a smaller diameter is rather high, due to this high point contact force. This may be acceptable for applications where the rod is being coiled only very few times and where the recoiled rod is kept on the reel by additional holders, but is not acceptable in applications where frequent coiling/uncoiling has to take place, which is the case in the technical investigations. An example of such applications is typically found in sounding apparatuses for determining the penetration resistance of the ground as a function of depth, both on land as below a sea floor.